The hitherto-known technology for producing 2-[6-(hydroxymethyl)-1,3-dioxan-4-yl]acetic acid derivatives includes the following processes.    (1) A process starting with 3-hydroxy-γ-butyrolactone to synthesize a 3,5,6-trihydroxyhexanoic ester derivative via a 3,5-dihydroxyhexanoic ester derivative (JP-A-04-173767).    (2) A process starting with 3,4-dihydroxybutyronitrile acetonide to synthesize a 3,5,6-trihydroxyhexanoic ester derivative via a 3,5-dihydroxyhexanoic ester derivative (JP-A-02-262537).    (3) A process starting with a 4-chloroacetoacetic acid ester to synthesize a 3,5,6-trihydroxyhexanoic ester derivative through benzyloxylation, reduction, chain extension and like steps. (JP-A-06-65226).    (4) A process starting with a 4-chloro-3-hydroxybutyric ester to synthesize a 3,5,6-trihydroxyhexanoic ester derivative through chain extension, reduction and like steps. (U.S. Pat. No. 5,278,313).    (5) A process starting with malic acid to synthesize a 3,5,6-trihydroxyhexanoic ester derivative via a 2,4-dihydroxyadipic acid derivative (JP-A-04-69355).
However, these processes involve ultra-low temperature reactions around −80° C. in some stage or other of the respective production processes (1, 2, 4 and 5) or a high-pressure hydrogenation reaction requiring a pressure of as high as 100 kg/cm2 (3), thus invariably requiring extraordinary reaction equipment. Moreover, expensive starting materials are used in some or other stages, so that none of the processes are efficient enough for industrial-scale production.